Public health officials are warning adults and adolescents to get booster shots in the wake of an unusually large number of cases of whooping cough this year around the nation and in Maryland.

More than 20,000 cases of the respiratory disease were reported in the first seven months of the year in the United States, almost 21/2 times the number in all of last year, according to the U.S. Centers for Disease Control and Prevention. The agency says there are likely many more cases that are not reported.

In Maryland, the CDC has preliminarily logged 125 cases this year, and state data show about a quarter of the cases are in infants too young to be vaccinated.

Washington State, with more than 3,000 cases, was the first to declare an epidemic in April, but CDC officials said so many states are logging large outbreaks that this could be the worst year for whooping cough since 1959.

Officials say outbreaks of the disease, officially called pertussis, are cyclical, though they can't say for sure what is causing this year's unusually high number of cases. They say it's possible the disease is being better diagnosed, and that the effectiveness of the vaccine, routinely given only to children, not adolescents and adults, is waning.

"The vaccine isn't perfect, but it's good," said Dr. Lucy Wilson, chief of the Center for Surveillance, Infection Prevention and Outbreak Response at the Maryland Department of Health and Mental Hygiene. "That's why we're advocating for boosters."

State and federal officials say anyone older than 6 months can get the booster, called Tdap, a combination vaccine with diphtheria and tetanus. Because cases are most dangerous to infants, officials strongly advise parents and other caretakers and pregnant women, as well as health workers, to get another vaccination.

More than half of children with whooping cough are hospitalized, Wilson said. One in five gets pneumonia and one percent die.

Small children generally get a series of five vaccinations, but officials say boosters should be given to 11- and 12-year-olds, the age when immunity appears to begin waning. Boosters aren't required for school in Maryland now, but will be in 2014, Wilson said.

Lisa Hubbard, a Carney mother of two, decided to have her children vaccinated regardless of the law. Joshua Hubbard, 11, got his shot Wednesday. She's also made sure her pregnant sister and sister-in-law know about the outbreak and protect themselves.

"To keep children safe you have to pro-actively get these shots and take that small risk of side effects, versus taking the bigger risk of a child contracting a highly contagious even deadly disease," she said. "It's our job to make decisions that are in the best interests of our children and all children."

The doctor who recommended the boosters to Hubbard was Dr. Scott Krugman, chairman of the department of pediatrics at MedStar Franklin Square Medical Center and the president of the Maryland Chapter of the American Academy of Pediatrics.

He said to protect children and the community at large, enough people need to be vaccinated: "Pediatricians are encouraging all teenagers to come in for their annual physicals to make sure they have received their Tdap booster shot, not only to protect themselves, but to protect vulnerable infants through herd immunity."

A problem doctors can have is that only adolescents tend to make the whooping noise associated with whooping cough, so the illness sometimes is mistaken for the common cold. Early symptoms are runny noses, congestion, sneezing and a mild cough and fever. The heavy coughing usually begins after a couple of weeks. CDC officials recommend antibiotics for treatment of the sufferer and for prevention in those who have come in contact with it.

Vaccine experts at the CDC and elsewhere still stand behind the vaccine, though some evidence suggests that a newer version is less likely to provoke immunity and could be linked to more cases.

The formulation was changed in 1997 to reduce side effects such as pain at the vaccination site, listlessness, prolonged crying and some other rare and serious complications in babies, said Dr. Andrea A. Berry, a pediatric infectious disease specialist at the University of Maryland School of Medicine's Center for Vaccine Development.

The older vaccine was made using the whole pertussis bacteria, which is grown and later inactivated. The newer one contains only individual antigens of the bacteria that still produce an immune response but with fewer side effects.

A recent study from Australia published in the Journal of the American Medical Association found children given the newer, "acellular" vaccine had higher rates of disease. But Berry said it doesn't explain the severity of this outbreak, and she's not advocating a return to the older vaccine.

"The vaccine is not perfect, but I would not recommend returning to the whole-cell vaccine," she said. "The acellular vaccine does provide protection and has a much better safety profile. The key is using it more broadly."

Already, she said that the vaccine has saved many from the disease. In the early part of the last century, before there was a vaccine, there were routinely 270,000 or more cases a year in the United States and 10,000 deaths. There are fewer deaths in modern times — only 10 so far this year and none in Maryland.

Others also are pushing boosters to continue to cut down on the illness and related deaths, including insurers. CareFirst BlueCross BlueShield, for example, makes sure doctors know that boosters are recommended for adolescents and adults, said Dr. Daniel Winn, the insurer's senior medical director.

He said vaccination rates are good for young children but not for older kids and adults.

"Rates of vaccination for older people, those over 50, are abysmal," he said. "That means the herd immunity is much less because not enough people are vaccinated."

Winn recommended that people ask their doctors about vaccinations in general because sometimes when other medical issues are more pressing such preventive steps can be forgotten.

He said swine flu and West Nile virus also are becoming problems in other states and people should be taking precautions. All recent cases of swine flu nationally appear to have come from contact with pigs, and at the upcoming Maryland state fair, Winn said, children should wash their hands frequently and avoid touching their faces.

Maryland recently recorded its first West Nile Virus case, and officials are recommending people avoid areas of high mosquito activity and outdoor activities at dawn and dusk when mosquitoes are most active. They also say wear long-sleeved pants and shirts and hat and use insect repellent.

Readers submit photos and information on medical professionals who have recently been promoted, hired or honored. Select photos will be published in the Health and Medicine section of Sunday's edition of The Baltimore Sun. Caption size is limited and only photos are accepted in this feature....